A lot of stores will do a few cuts for free, but they always warn you they are doing "rough cuts", NOT super-accurate. Typically they use a large saw frame system that is not really as rigid as a big table saw. They do their best to measure and get it right, but accuracy of +/- 1/8" may be all you can expect. Do not expect cabinet-making accuracy or straightness. And for speed, they often are using a rip saw or combination blade, so the cut is not a clean as a fine-toothed blade for cabinet work.